The field of developmental genetics has accumulated a large body of evidence which indicates that genes exert control over all phases of development of the embryo. The question of how a given gene (or gene set) is brought to expression is one part of the embryo, while in another portion of the embryo that very same gene is inactive, constitutes the most basic research problem in the field of cellular differentiation. During the past 5 years several new insights have been gained into the issue of how differential gene expression in the early embryo is accomplished. These include: (a) identification of various cytoplasmic components which contribute to the pattern of early embryonic gene expression; (b) analyses of the population of mRNA which support early development; (c) isolation of specific genes which are active in early development; and (d) nuclear transplantation analyses of the developmental potential of nuclei. This conference will bring together scientists who represent a wide spectrum of experimental approaches, and will include the embryologists, biochemists, and molecular biologists who have made the important new discoveries listed above.